Recalibrating your speedometer

Any time you install larger tires and/or new gears, your speedometer and odometer will need to be recalibrated so they read correctly with your new setup. The following article will guide you through choosing the correct speedometer gear and then installing it. This information is for XJ’s and TJ’s, but should apply to ZJ’s and YJ’s as well.

The chart below was put together by my friends over at Raingler.com and it’s the most accurate chart I’ve found. The numbers in the white boxes are the number of teeth on the speedo gear that you’ll need for a given tire and gear combo. For instance I’ve got 35’s and 4.56 gears, so I need a 37-tooth speedo gear.

R&P / Tire 38″ 37″ 36″ 35″ 33″ 32″ 31″ 30″
5.13 38 39 40 41 43 45 46 48
4.88 36 37 38 39 41 43 44 46
4.56 34 35 36 37 39 40 42 43
4.11 31 32 33 34 36 37 38 40
3.73 27 28 28 29 31 32 33 34
3.55 31 31 32 33
numbers in bold are GPS-verified accurate

Once you’ve determined which gear you need, simply tack the tooth number onto the back of 520676 to get the Jeep part number to give to your parts guy. So for that 37-tooth gear I needed, I ordered p/n 52067637. If you’ve got a ’91 or older XJ with the mechanical gauges, check out the Speedometer Re-calibration article on JeepsUnlimited.com to determine the correct part number for your application, the install is just the same though.

Once you’ve got the gear, it’s time to install it. The speedo gear housing is located on the left side of your transfercase’s tail housing. There’s a wishbone shaped retainer plate that holds the speedo gear housing in the t’case, you’ll need to unbolt it before you can remove the gear housing.

Now pull the gear housing straight out of the t’case. The gear then pulls out of the end of the gear housing. It’s snapped in place, so it may take a good tug to pop it out.

The gears are different sizes and colors, based on the tooth count. Here you can see the 39-tooth gear on the left that I was running with my 33’s, and the new 37-tooth gear on the right. The new gear simply slides into the housing and snaps into place.

Now here’s the slightly tricky part… because the different gears are different sizes, the housing is offset and needs to be put back into the t’case in the correct orientation, otherwise it either won’t fit or you speedometer and odometer won’t work. The outside of the gear housing has number ranges embossed on the side, when you put the housing back into the t’case, it needs to be installed such that the number range containing your gear’s tooth count is aimed down and to the back as shown in the pic above. There are notches in the housing that the retainer plate hooks into to ensure the housing is oriented correctly and doesn’t shift once the retainer plate is installed. Tighten the retainer plate bolt back down and enjoy your newly corrected speedometer and odometer!

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  1. speedometer calibration - JeepForum.com August 30th, 2010 6:12 am

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